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Fuel pressure test.
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Supporting Member of 12/20
Picture of Paul And Jaime
Hello all. I need to do a fuel pressure test and I was curious what type of fitting I would need. Thought the best place would be at the quadrajet but not sure of the thread size. I have see some say its 7/8 20 so I guess I would need a female 7/8 20 to a barb fitting? Is there a better way to do this, like at the mechanical fuel pump where the fuel line attaches? wonder what thread size that will be. Thank all
Posts: 152 | Location: Ky | Member Since: 10-20-2020Reply With QuoteReport This Post
Official Barth Junkie
Supporting Member of 1/23
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The desired pressure for the the Qjet is 4-6 psi. For such low pressure, you could probably cobble some kind of T in the line with rubber hoses for temporary measurement. For something more durable you could cut the metal fuel line and install a brass T with flare fittings. In any case be VERY careful of fuel leaks in the hot engine doghouse. confusion

When I first got my Regal in 2011, I had nothing but fuel problems. Tiny filter in the Qjet plugging, intank fuel pumps failing, mechanical fuel pump problems, rusted lines, etc. In the long run I replaced everything from the tanks forward. Removed sock filters in tanks, bypassed intank pumps, installed large primary filters near tanks, installed a frame mount electric fuel pump, replaced fuel selector valve, replaced all fuel lines and hoses, removed mechanical fuel pump, installed second filter near carb. Nothing but trouble with the GM stuff. The stock system is barely adequate at best to supply a thirsty 454 and is prone to vapor lock.

After almost everything else was replaced I finally got smart and dumped the carb. I installed an electronic throttle body fuel injection system (TBI), braided stainless lines in the doghouse and a 20 psi electric rear frame fuel pump. The older low pressure TBI systems regulated pressure to 11-13 psi and always ran perfectly for me.

In the process of troubleshooting these many problems, the most valuable gauge I had was the fuel pressure gauge. No reason to work on anything up front if the fuel pressure was too low, as it often was with the stock fuel system.

There is a discussion of fuel gauges in one of my old threads from 2012. Numerous concerns about rubber lines, hose clamps, and fuel leaks, all legitimate concerns.

However, as stated above, the fuel pressure gauge saved me lots of wasted time chasing fuel starvation isssues. In spite of the many warnings, I had a fuel pressure gauge in the Regal for all the time I owned it, put over 40,000 miles on it and never had any problems. To be sure, I inspected (and modified) it very often.

gauge link here:

It was the most useful gauge I had in the Regal. With careful installation and maintenance, it was not a problem for me.

tanks and filters here:

selector valve thread:

"Final solution" = fuel injection!

Good luck with your thirsty 454! Mechanic Thumbs Up

"98" Monarch 37
Spartan MM, 6 spd Allison
Cummins 8.3 325+ hp
Posts: 5098 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
Supporting Member of 12/20
Picture of Paul And Jaime
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Ok so what size thread is the inverted flare fitting that goes into the fuel filter housing ? I guess on the fuel pump side it is a 3/8 npt? I don't mind cutting the fuel line and putting in a T for a fuel gauge but not sure what to order. I assume the fuel line is 5/16 ? ahhhh so many numbers...
Posts: 152 | Location: Ky | Member Since: 10-20-2020Reply With QuoteReport This Post
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